Metastable isotactic polystyrene prepared by freeze-extracting concentrated solutions in solvents of middle molecular size

The morphology and crystallization behavior of freeze-extracted isotactic polystyrene (iPS) derived from concentrated solutions in solvents of middle molecular size were characterized by the wide-angle X-ray diffraction, infrared spectroscopy, and differential scanning calorimetry. It was found that the freeze-extracted iPS sample is poorly crystallized, but the chains are in an ordered 31 helix conformation, which can be easily transferred to a highly crystalline state upon heating. It can easily crystallize even cooled from the melt. The ordered 31 helix structure could be maintained even after melting at 520 K, which is 30 K higher than the melting point, but diminished at 530 K. The metastable property of the freeze-extracted sample from concentrated solutions in solvent of middle size can be attributed to fewer interchain entanglements, like the behavior of collective particles from very dilute solution in benzene.